In the development of radio communication systems, in particular cellular communication (like for example GSM (Global System for Mobile Communication), GPRS (General Packet Radio Service), HSPA (High Speed Packet Access), UMTS (Universal Mobile Telecommunication System) or the like), efforts are made for an evolution of the radio access part thereof. In this regard, the evolution of radio access networks (like for example the GSM EDGE radio access network (GERAN) and the Universal Terrestrial Radio Access Network (UTRAN) or the like) is currently addressed. Such improved radio access networks are sometimes denoted as evolved or advanced radio access networks (like for example the Evolved Universal Terrestrial Radio Access Network (E-UTRAN)) or as being part of a long-term evolution (LTE) or LTE-Advanced, also generally referred to as International Mobile Communications-Advanced (IMT-A). Although such denominations primarily stem from 3GPP (Third Generation Partnership Project) terminology, the usage thereof hereinafter does not limit the respective description to 3GPP technology, but generally refers to any kind of radio access evolution irrespective of the underlying system architecture.
In the following, for the sake of intelligibility, LTE (Long-Term Evolution according to 3GPP terminology) or, specifically, LTE-Advanced is taken as a non-limiting example for a radio access network of cellular type being applicable in the context of the present invention and its embodiments. However, it is to be noted that any kind of radio access network of cellular type, such as GSM, GPRS, HSPA and/or UMTS, may likewise be applicable, as long as it exhibits comparable features and characteristics as described hereinafter.
As a particular example, the present invention is applicable to 3GPP 36 series standards.
In the development of cellular systems in general, and access networks in particular, cellular network systems are proposed as one concept. In the context of LTE or LTE-Advanced, cellular networks, the cells are typically deployed by base stations denoted as evolved Node_B's (eNBs) (also referred to as radio transceiver). The network environment, i.e. the base stations and/or cells defined by those may be implemented by the same or different radio access technologies.
Generally, in such cellular networks, a terminal or user equipment UE is served by a cell defined by a base station. In case of a moving/roaming terminal, however, a terminal has to know to which other (neighboring) base station or cell it can be handed over. Therefore, the terminal receives also some signals from another base station. Hence, a terminal may also be “resident” in the coverage of more than one cell, i.e. in the coverage of its serving cell and some neighboring cells.
In such scenario, and related to LTE-Advanced standardization, it has been discussed whether data transmission from multiple cells towards one terminal should be supported; this is denoted as “Coordinated Multipoint Transmission” (COMP).
So far, 3GPP only discussed very general aspects related to this topic. In the recent discussions in 3GPP related to CoMP, the main concern in terms of feasibility of CoMP arises from the fact that very fast (practically zero-delay) communication is required between the cooperating radio transceivers or base stations, eNBs.
This issue can be avoided by restricting the CoMP operation to take place within one base station eNB, e.g. between different cells defined due to multiple antennas of the base station. (Sometimes, such a cell may also be referred to as sector).
However, many terminals UE might be located in the gray area between CoMP operation and single cell transmission (SiC) operation.
Hence, it is thus difficult for the base station or the radio network controller to decide on the mode of operation, SiC or CoMP, for the terminals it is serving and/or for the terminals within the base station's coverage but not assigned to the base station as a serving base station.
The main discussion in 3GPP in terms of CoMP so far focuses on independent per-cell feedback. That is, any decision is uniformly applied to the cell, i.e. at least to all the terminals served by the cell. Optional inter-cell adjustment and/or joint feedback is also discussed.
Joint feed back refers to the case when a single UE feed back the CSI assuming joint transmission from multiple cells. So the single UE sends the feedback typically to a single serving cell. One option could be to define that a UE provides a channel state indication, CSI, feedback for both the SiC mode and the CoMP mode simultaneously, or to have those two reports feeded back alternatingly in time in a predefined manner. This, however, would be clearly suboptimal solution since only half of the reports would actually contain relevant information for the eNodeB.
Thus, according to one aspect of the current discussion on this topic, the base station or radio resource control needs to decide partly blindly on the SiC or CoMP mode for the terminals served and/or within its coverage. This will most likely result in non-satisfactory operations due to possibly inadequate decisions.
Moreover, according to another aspect of the current discussion on this topic, the amount of information to be fed back from a terminal blocks processing resources of the terminal to acquire all this information and in particular will overload the assigned signaling channels which may need to carry also other necessary information.
Accordingly, there is a demand for mechanisms to be implemented in methods and apparatuses, for improving scenarios in which a terminal may communicate in a single cell transmission mode (SiC) as well as in coordinated multipoint transmission mode (CoMP).